The present invention relates generally to an apparatus and method for modifying the shape and refractive power of the cornea, and more particularly, to removing a section of precise shape from a corneal button. (The term "corneal button" is used here and in the following description to refer to any disc-like or toroidal section of corneal tissue or other material such as soft contact lenses. It normally is lamellar and a partial thickness section of the cornea but need not be either).
The curvature of the anterior surface of the cornea, and thus its refractive power, may be modified by altering the shape of a corneal button and fixing the resultant to the cornea. One method to accomplish this, referred to as Keratomielusis, is to remove a lamellar (partial thickness) corneal disc from the patient's eye, machine out a section from the posterior surface using a specially adapted contact lenses lathe after freezing the corneal button, and returning it to the patient's eye. This approach has several drawbacks. The freezing can kill or damage the corneal tissue, and slows the patient's recovery. Further, freezing changes the thickness of the corneal button making accurate prediction of the final refractive correction difficult. Also, the machining operation, despite the freezing, is traumatic and can damage the corneal tissue. In addition, inaccuracies inherent in the lathe machining process (vibration, run-out, low surface cutting speed, etc.) limit the accuracy of the process. Furthermore, securing the corneal button in place by freezing is unreliable. Further, the modification is limited to relatively simple spherical shapes. Also, adjustment and operation of the apparatus is complicated and the procedure time-consuming.
There are three modifications of this procedure. In one, referred to as Homoplastic Keratomielusis, the corneal button is removed from the patient's eye as before, but now a donor corneal button is modified by the above procedure and sewn on the patient's eye. In another, referred to as Keratophakia, the corneal button is removed from the patient's eye as before, a donor corneal button modified by the above procedure, and the donor button inserted behind the patient's corneal button which is then sewn in place. In the third, referred to as Epikeratophakia, no corneal button is removed. Instead, a donor corneal button is prepared by the above procedure and sewn on over the patient's own cornea. All these methods employ the same freezing and lathe machining procedure, and thus suffer from all the same drawbacks cited above.
The prior art teaches the broad concept of deforming corneal tissue lens over a mold and altering its diopter by a planar cut as illustrated by Jose I. Barraquer, M.D. in the Arch. Soc. Amer. Oftal. Optom. (1967) 6-21 beginning particularly at page 54 through page 60. Barraquer teaches in this context the employment of the "congelation plate" to the microtome to freeze the tissue prior to cutting.
The Corning Glass Works of Corning, N.Y., have developed microporous glass for fixation of tissue by suction as taught at page 611 of a reprint from The Cornea, Work Congress, Washington; Butterworth's 1965, starting at page 605. The microporous glass is designed to create suction by capillary action and not by the application of the mechanically produced vacuum.
It is an object of this invention to provide an improved method of holding and distorting tissue during sectioning without the need of freezing or applying mechanical or chemical trauma to the tissue. The present invention permits immediate section of a corneal button for autoplastic surgery as well as homoplastic surgery without the time delay and trauma of mechanical or thermal (cryogenic) preservation.
The present invention circumvents these difficulties and is described below.